This invention relates generally to axial flow or propeller type fans. More specifically, the invention relates to a fan blade having an enhancement at its tip that is effective in reducing or preventing separated air flow around the blade tip and thus reduces radiated noise from the fan.
Axial flow fans are widely used to move air in a great many applications. Such fans are common in heating, ventilation, air conditioning and refrigeration systems. A primary objective in the design of most fans is to reduce the noise produced by the fan when it is in operation.
As an axial flow fan moves air, and due to the pressure difference between them, air moves from the pressure surface to the suction surface of the blade over the blade tip. The flow forms a vortex on the suction side of the blade in the region of the blade tip. Within the core of the vortex the air is turbulent. One source of the turbulence is the flow separation caused by the sudden reversal of the air flow around the relatively sharp tip of the fan blade. The interaction between the turbulent air in the core of the vortex and the blade tip is a source of air flow noise from the fan.
What is needed is a means of reducing the tip vortices on the blades of an axial flow fan in order to reduce the interaction between vortex and blade tip and thus reduce fan radiated noise.